Just make it apply on use already (and apply to the PLD) ... when Divine Veil was the only Tank shield it made some sense for it to be 'special', but now that the other Tanks all have an instant shield / party mitigation the heal requirement is simply antiquated and clunky.
Either that or have the heal apply part of its potency to the shield, so at least there would be a reason for the heal requirement (though that may be verging on spread crit-lo territory)
They could allow oGCD heals proc veil also, but in some niche situations as is currently is, you can pop veil 30seconds in advance and have it proc'd just before it wears off, and allow a second veil 60 seconds later. This doesn't always go to plan, either recieve a gcd heal before it's intended, or embrace, or is just simply missed.
Personally though I rather it be press, everyone has a shield and be done instead of being convoluted compared to current tank AoE mitigation.